Evidence: Eggs, late summer and autumn larvae have been systematically monitored on the same trees in and around Savernake Forest for three years (habitat conditions appear to have remained stable). Data: 2009 = 141 found, 2010 = 56, 2011 = 24 (corrected figures, 31/1/12). A similar trend has been noted in other districts where systematic searches have taken place, including Alice Holt Forest (Hants), north Bernwood Forest area (NW Bucks), Fermyn Woods (Northants) & Southwater Forest (W Sussex).
Also, I seem to have recorded higher autumn larval mortality in 2012, but there is considerable difference between the three sample sizes and I'm not sure what constitutes a valid sample here. It appears that larval losses (to assumed predation) are higher in dry autumns, such as that of 2011, as hiding in the rain drop that gathers at the leaf tip seems to be a sound strategy for survival. Predation may be lower in wet autumns.
All shall be revealed... But first we have to get through this pointless winter...
The weather forecasters are predicting a cold first half of February. That makes sense to me as Marsh Fritillary larvae have, surprisingly, yet to come out of hibernation here in S Glos. I've recorded their emergence from hibernation for the last 17 years quite accurately. The running mean for the first appearance date is 23rd Jan. Even in Jan 2011, after the coldest December on record, they were first noted on the 19th. The present winter has so far been the mildest in my 18 year study (and one of the driest). Now, do aurinia larvae know something we don't?????